Typical Internet search engine websites, such as one provided by Lycos, Inc., enable users to conveniently locate websites relating to a particular topic without having to know a uniform resource locator (URL) for the website. In particular, a user enters search terms as a query to a search engine and receives a list of results, typically in the form of hyperlinks to each identified website along with a title, description, and/or an excerpt of the website. Search engine websites generally use proprietary algorithms for performing automated searching and/or indexing of documents available over the Internet. The purpose of such algorithms is generally to locate web documents that are relevant in the context of a particular query based on the content of the web documents. Accordingly, results can be ranked and presented to the user in an order of relevance, as determined by the particular proprietary algorithm.
Many Internet search engines also provide predetermined results based on the search terms included in the query and without explicitly considering the content of the web documents included in the results. For example, the results of a search may include sponsored links or other paid listings that are based on an inclusion in the search of a particular keyword or keywords. Typically, an advertiser bids or pays a preset fee to be displayed as a sponsored link for searches that include a particular keyword or keywords. In many cases, advertisers bid based on a pay-per-click model, in which the advertiser only pays when its link in a search results list is clicked.
The efficiency of a paid listing for a website is dependent upon the selection of one or more keywords that are most likely to be used by consumers to which the website is targeted. For example, a website operator may want its website to appear as a paid listing in response to search queries submitted by consumers who are actually searching for the content of the website or some closely related content. Keywords can be selected by identifying a small number of highly relevant search terms and using a keyword expansion technique. Conventional keyword expansions are lexicographical and use thesauruses, dictionaries, and other linguistic resources to identify alternative search terms with the same or similar meanings.